The invention relates to a unit of an electric lamp and a reflector, comprising
a reflector body including a reflector part with a concave reflecting surface having an optical axis, and a hollow neck-shaped portion and a light emission window surrounding said optical axis and integral with said reflector body; PA1 an electric lamp comprising a light-transmitting lamp vessel sealed in a vacuumtight manner, enclosing a cavity and having, a first and a second mutually opposing sealed end portion, an electric element arranged in the cavity and respective current conductors connected to the electric element, extending through said sealed end portions and issuing from the lamp vessel to the exterior,
the electric lamp being fixed in the reflector body with the first end portion inside the neck-shaped portion, While the cavity lies within the reflecting portion and the electric element is on the optical axis.
A similar unit of electric lamp and reflector is known from EP 0 595 412, U.S. Pat. No. 5,506,464.
The known lamp and reflector may be used for projection purposes, such as film or slide projection, but also in projection-television sets. In these projection television sets there is, just like film and slide projection, in a plane perpendicular to the optical axis of the reflector a light transmitting picture carrier, for example, an LCD screen or a DMD (Digital Mirror Device) screen. Such picture carriers are generally rectangular, for example, having an aspect ratio of 4/3 or 16/9.
The object of the unit of electric lamp and reflector is to clearly light the picture carrier substantially uniformly, so that an optical system which may contain a projection lens can display the image in a clear and uniform manner on a screen so as to have it watched.
The uniformity of the lighting, however, may be adversely affected by an inaccurate positioning of the unit in the optical system. The alignment of the unit in the optical system is generally effected by means of pressing a transparent plate closing off the reflector against a reference face of the optical system. During this operation, scratches may appear on the transparent plate which are detrimental to the clarity of the lighting. If no transparent plate is present, the alignment is effected by means of a pressing flange on the side of the light emission window. Detrimental to the alignment with the aid of the transparent plate and/or the pressing flange is that they are to be flat because otherwise the orientation of the unit relative to the reference face in the optical system may vary.
The positioning of the unit in the optical system requires some clearance for maneuvering. The unit may change place in the optical system, for example, as a result of differences in expansion at high operating temperatures, because when the unit is fixed in the optical system, it is possible for a displacement to occur in a plane transverse to the optical axis of the unit. This clearance may lead to an unfavorable situation during operation of the device in which situation the optical axes of the unit and the optical system no longer coincide, which has a detrimental effect on the clarity and the degree of uniformity of the lighting.